Recently 875 cases (4 fatal) of eosinophilia-myalgia-syndrome (EMS) has been reported in the U.S.A. There appears to be an association with ingestion of tryptophan or certain lots of tryptophan. The purpose of this study is t 0 determine if one or more of the several lots of L-tryptophan submitted by the Center of Disease Control (CDC) has the potential to cause toxicity in female B6C3F1 mice. Mice were given L-tryptophan in 0.5% methylcellulose-water at doses of 0 or 300 mg/kg B.W. daily from Monday to Friday for 21 days over a 30-day period by gavage. Animals were killed at 3, 17 and 30 days after the first treatment. Multiple hematological and clinical pathology examinations were performed during the dosing with histopathological and hematopoietic evaluations at the terminal sacrifice. The results of this study provided no indication of toxicity in mice that could be interpreted as related to the EMS as seen in man. The B6C3F1 mouse may not be a sensitive model or the lots tested may not contain the contaminant(s) that causes EMS in man.